You can carry marijuana in a vehicle in Montana if you are 21 or older or hold a medical card, but an opened package cannot ride in the passenger area on a highway, and nobody in a moving vehicle may use it. The storage rule works much like the open container law for alcohol. This page explains both rules and their penalties. It is part of our Montana DUI Guide.
Transporting Marijuana Is Lawful Within Limits
Under MCA § 16-12-106(1)(a), a person who is 21 or older, or a registered cardholder, may possess, purchase, use, and transport 1 ounce or less of usable marijuana. Within that ounce, not more than 8 grams may be in concentrated form, and not more than 800 milligrams of THC may be in edible products meant to be eaten or swallowed in solid form.
The statute says these acts may not be an offense under state or local law and may not be "a basis to detain, search, or arrest." All of that is expressly "subject to the limitations in 16-12-108," which include the vehicle rules below.
The Passenger Area Rule: MCA § 61-8-1027
A person commits the offense of unlawful possession of marijuana in a motor vehicle if the person knowingly possesses marijuana, marijuana products, or marijuana paraphernalia "within the passenger area of a motor vehicle on a highway."
Two definitions set the reach of that rule. The passenger area is the area designed to seat the driver and passengers, plus any area readily accessible to them while seated, "including an unlocked glove compartment" (MCA § 61-8-1001(13)). A highway is a publicly maintained way open to the public for vehicle travel (MCA § 61-1-101). A center console, a door pocket, a cup holder, and a bag on the back seat are all within the passenger area as the statute defines it.
Note that the statute covers paraphernalia as well. A used pipe in the console falls under the same rule as the marijuana itself.
Where the Statute Says You May Keep It
Section 61-8-1027(2) lists five situations the offense does not apply to:
| Marijuana, products, or paraphernalia that is | MCA |
|---|---|
| Bought from a dispensary and still in its unopened, original packaging | § 61-8-1027(2)(a) |
| In a locked glove compartment or storage compartment | § 61-8-1027(2)(b) |
| In the trunk or luggage compartment, or in a truck bed or cargo compartment | § 61-8-1027(2)(c) |
| Behind the last upright seat of a vehicle that has no trunk | § 61-8-1027(2)(d) |
| In a closed container in an area not normally occupied by the driver or a passenger, in a vehicle that has no trunk | § 61-8-1027(2)(e) |
The first exception is the one most people rely on without knowing it: a sealed purchase on the way home. It refers to marijuana "purchased from a dispensary," so it does not describe home-grown marijuana or a jar that has been opened. For those, use the trunk or a locked compartment.
Unlike the alcohol open container law, the marijuana statute has no exception for passengers in a hired bus, taxi, or limousine, or for the living quarters of a camper or motor home.
The Penalty Is a Fine, Not a Criminal Record
A conviction carries a fine of not more than $100 (MCA § 61-8-1027(3)(a)). The statute then limits the consequences. A violation is not a criminal offense within the meaning of several listed statutes, it "may not be recorded or charged against a driver's record," and an insurance company may not hold it against the insured or increase premiums because of it. The standard court surcharges may not be imposed.
This is a different offense from DUI in every respect. It does not suspend a license, and it is not a prior for any later DUI.
Using Marijuana in a Moving Vehicle
Montana's marijuana chapter does not permit consumption in a vehicle that is being operated, by anyone in it. Section 16-12-108(1) excludes from the chapter's protection:
- consumption of marijuana or marijuana products while operating or being in physical control of a motor vehicle while it is being operated (subsection (1)(b)); and
- smoking or consuming marijuana while riding in the passenger seat within an enclosed compartment of a motor vehicle while it is being operated (subsection (1)(c)).
Subsection (2) of that section assigns specific penalties to some of the listed limitations, but not to these two. In practice an opened product in the passenger area is a violation of § 61-8-1027, and a driver who has been using faces the much more serious question of DUI. A passenger's use does not make the driver guilty of DUI, but smoke in an enclosed car is something an officer will note about everyone inside.
Drivers and Passengers Under 21
The lawful-transport rule applies to adults 21 and over and to registered cardholders. The marijuana chapter does not permit possession or transport by a person under 21 unless that person is a cardholder, or is at least 18 and working for a licensed marijuana business (MCA § 16-12-108(1)(g)). Possession by a person under 21 is punished under a separate statute, MCA § 45-5-639.
For driving, a person under 21 commits an offense with any amount of active THC in their body (MCA § 61-8-1002(1)(e)(ii)). Our under-21 DUI page explains that rule.
How a Storage Ticket Turns Into a DUI Case
Most people who are cited under § 61-8-1027 pay a small fine and move on. The risk is what the same facts suggest to an officer. An open package, a warm pipe, or smoke in the car can lead to questions about recent use, roadside tests, and a request for a blood sample. Whether the stop could lawfully be extended that far depends on the facts, and our pages on vehicle searches during a DUI stop and how long THC stays in your blood cover what comes next.
This page covers Montana state law on state and local roads. Federal land follows federal rules, which our page on DUI in national parks addresses.
This page explains Montana law in general as of the 2025 Montana Code Annotated. It is not legal advice about your specific case.